Media for water treatment

ABSTRACT

The present invention relates to compositions for water treatment based on biodegradable polymers containing repeating succinyl units, biocidal oxidizing agents and unsubstituted or substituted amidosulphonic acid, their use in, and the process for, conditioning water of cooling circuits.

This application is a 371 of PCT/EP 99/05640, filed Aug. 4, 1999.

BACKGROUND

The present invention relates to compositions for water treatment basedon biodegradable polymers containing repeating succinyl units, biocidaloxidizing agents and a substituted or unsubstituted amidosulphonic acid;their use in, and the process for, conditioning water of coolingcircuits.

When natural waters are used for industrial purposes, for example ascooling water, the water used is changed physically and/or possibly alsochemically specifically or unintentionally. Thus, for example in openrecirculating cooling systems, temperature changes, concentration and apH increase due to the discharge of carbon dioxide in the cooling towerare unavoidable.

Due to the concentration and increase in pH from the discharge of CO₂,the concentration of hardness constituents, in particular calcium ionsand carbonate ions, increases. If the natural waters were in equilibriumbefore use (lime-carbon dioxide equilibrium), an increase inconcentration of the hardness constituents leads to supersaturation. Toprevent scale deposition (encrustations), in particular on heat-transfersurfaces, treatment of the waters by addition of additives (“scaleinhibitors”) is necessary.

A further, sometimes even the predominant, purpose of the use ofadditives in water treatment is protection of metallic materials againstcorrosion. For example, when unalloyed carbon steels are used in openrecirculating cooling systems, adequate corrosion inhibition is desired,since the conditions prevailing in such systems (oxygen saturation, saltaccumulation) lead to an acceleration of corrosion.

WO 97/39078 proposes the use of biodegradable polymers, such as, forexample, polyaspartic acid, or other aspartic-acid-containing polymersin combination with biocidally acting oxidizing agents to conditionwater in, cooling circuits.

Descriptions are given, inter alia, of experiments in which 10 mg/l ofpolyaspartic acid having a molecular weight of about 3000 were tested inthe presence of 0.4 mg/l of sodium hypochlorite for scale-inhibitingactivity, and no decrease in scale-inhibiting activity was observed overthe measurement period of 4 hours. When 0.4 mg/l of a mixture of sodiumhypochlorite and sodium hypobromite in a weight ratio of 1:1 was added,95% of the initial activity was still present after 4 hours.

Furthermore, in a cooling circuit having a cooling tower, theconcentration of polyaspartic acid was tested without and with additionof 0.2 mg/l of chlorine in the form of sodium hypochlorite over onemonth: without chlorine addition, with daily doses of 20 to 50 mg/l ofpolyaspartic acid, a concentration of between 11 mg/l and 2 mg/l wasestablished, and with chlorine addition a concentration of about 20 m/lwas established.

A disadvantage of the mixtures of WO 97/39078 is the fact that thepolymers used there react to a considerable extent with microbicidessuch as chlorine, bromine or halogen-releasing products, which isobservable by a decrease in the biocide concentration.

It must be expected that owing to the reaction with the biocide,portions of polyaspartic acid are also destroyed, and that, as a result,the desired scale-inhibiting and/or corrosion-inhibiting activity is nolonger achieved.

In many cases, although it would be possible to create a compensation atleast to a certain extent by a higher dosage of the polyaspartic acid,the economic efficiency of the use of polyaspartic acid would suffer.

Therefore, the object of the present invention is to provide acomposition for water treatment based on polymers containing repeatingsuccinyl units, the components of which polymers remain stable over along period, so that the use is economically justifiable, even incooling circuits, especially in those having relatively long residencetimes.

DESCRIPTION

The object was achieved by means of the fact that polymers containingrepeating succinyl units are mixed with biocidally acting oxidizingagents and, as stabilizer, unsubstituted or substituted amidosulphonicacid is added. The stabilizer here has the task of preventing orsubstantially reducing the reaction between polymer and oxidizing agent.

Although the use of ammonia, amines, amides or amidosulphonic acids asstabilizers for chlorine is disclosed by U.S. Pat. No. 4,711,724 andU.S. Pat. No. 3,170,883, and U.S. Pat. No. 4,642,194 describes the useof amidosulphonic acids and organic sulphonamides (EP-A 0 569 220) asstabilizers for specific phosphonic acids with respect to chlorine andU.S. Pat. No. 4,759,852 also with respect to bromine, the use ofamidosulphonic acid and organic derivatives of amidosulphonic acid forstabilizing polyaspartic acid with respect to chlorine and bromine, hasnot previously been mentioned in the literature.

The high efficacy of amidosulphonic acid for stabilizing halogen withrespect to polymers containing repeating succinyl units is surprising tothose skilled in the art, since amide structures are present in thepolymers themselves. The addition of a further amide should thereforegive rise to the expectation of little activity. Surprisingly, by thismeans, the reaction between oxidizing biocide and polymer wasconsiderably reduced.

The present invention therefore relates to the use of polymerscontaining repeating succinyl units, in particular polyaspartic acids,as compositions for water treatment in combination with a biocide andamidosulphonic acid H₂NSO₃H or organic derivatives of amidosulphonicacid, and to the use of these compositions for water conditioning ofcooling circuits.

The polymers used according to the invention have repeating succinylunits having one of the following structures:

In addition, as a result of suitable reaction procedure and choice ofstarting materials, further repeating units can be present, e.g.

a) maleic acid units of the formula

b) maleic acid and fumaric acid units of the formula

The chemical structure is preferably analysed by ¹³C-NMR, FT-IR and,after total hydrolysis, by HPLC, GC and GC/MS.

Many preparation processes produce not the pure acids, but initially thecorresponding anhydrides, for example polysuccinimide (=PSI).Polymerization products of this type can be converted into a salt of PAAby reaction with a base in the presence or absence of water. Thisconversion of PSI polymers to PAA polymers takes place subsequently in asuitable apparatus by hydrolysis. Preference is given here to a pHbetween 5 and 14. Particularly preferably, a pH of 7 to 12 is selected,in particular by adding a base. Suitable bases are alkali metalhydroxides and alkaline earth metal hydroxides or alkali metalcarbonates and alkaline earth metal carbonates, such as sodium hydroxidesolution, potassium hydroxide solution, soda or potassium carbonate,ammonia and amines such as triethylamine, triethanolamine, diethylamine,diethanolamine, alkylamines etc. Particular preference is given, inaddition to the free acids, to their Na, K or Ca salts.

The temperature during the hydrolysis is suitably in a range up to andincluding the boiling point of the PSI suspension and is preferably 20to 150° C. The hydrolysis is carried out under pressure, if appropriate.

However, it is also possible to obtain the free polyaspartic acid bypurely aqueous hydrolysis or treating the salt with acids or acidicion-exchangers. The term “polyaspartic acid” (=PAA) for the purposes ofthe present invention likewise includes the salts, unless explicitlystated otherwise.

The final polyaspartic acid or the salts of polyaspartic acid areobtained by drying, preferably spray-drying.

Preferred polymers have a molecular weight, according to gel-permeationchromatography, of MW=500 to 10,000, preferably 700 to 5000,particularly preferably 1000 to 4500. Generally, the beta-form contentis more than 50%, preferably more than 70%.

The concentration of the polyapartic acids to be used for the watertreatment is usually approximately 0.5 to 100 mg/l of active compound inthe aqueous phase, but mostly in the range from approximately 2 to 50mg/l.

To achieve the object of the present invention, in addition, biocidesare used. Preferably, use is made of biocidal oxidizing agents having astandard redox potential more positive than oxygen.

Standard redox potentials, also termed standard potentials, aregenerally known thermodynamic terms, which are described in textbooks ofgeneral or physical chemistry. An example which may be mentioned ischapter 11 of the textbook: H. R. Christen “Grundlagen der allgemeiftenund anorganischen Chemie” [Principles of General and InorganicChemistry], Verlag Sauerländer-Salle, 1973. This textbook, on pages 692to 697, contains a list of different standard potentials, which can alsobe found in many other textbooks and tabulations. The magnitude of thestandard redox potential is usually expressed in volts.

Preferably, for the application according to the invention, oxidizingagents having a standard redox potential greater than 0.4 volts areused. Preferably, the oxidizing agent selected is hydrogen peroxide,chlorine, bromine, chlorine dioxide, hypochlorites, hypobromites orozone. Since these chemicals in the presence of water can participate inacid-base reactions and/or disproportionation reactions, theabovementioned oxidizing agents are also taken to mean their reactionproducts with water.

The biocides are used in the compositions according to the invention forwater treatment in concentrations of 0.05 to 20 mg/l. Preferably 0.05 to10 mg/l, especially preferably 0.1 to 5 mg/l, of biocide are used.

As stabilizers of the biocides, use is made of unsubstituted orsubstituted amidosulphonic acids of the formula (I)

where

Z represents hydrogen, lithium, sodium, potassium, magnesium or calciumand

R represents an unsubstituted or substituted radical from the groupconsisting of OH, C₁-C₄-alkyl, C₁-C₄-alkoxy, amino,mono(C₁-C₄-alkyl)amino, di(C₁-C₄-alkyl)amino, formylamino,—NHC(O)C₁-C₄-alkyl, —NHC(O)OC₁-C₄-alkyl, C₂-C₆-alkenyl, C₂-C₆-alkinyl,C₃-C₇-cycloalkyl, unsubstituted or substituted phenyl, naphthyl,pyridyl, pyrimidyl, pyrazyl, pyridazyl, pyrrolyl, imidazolyl, pyrazolyl,triazolyl, tetrazolyl, suitable substituents in each case being:C₁-C₄-alkyl, C₁-C₄-alkoxy, C_(1-C) ₄-alkoxycarbonyl, halogen, nitro,nitrilo, carboxyl, —S(O)_(n)C₁-C₄-alkyl where n=2 and each of which isoptionally substituted on the nitrogen by one or two C₁ ⁻-C₄-alkylgroups, sulfamoyl, —SO₂N(R¹)R² where R¹ and R² each denote C₁-C₄-alkyl.

Preferably, use is made of an unsubstituted or substitutedamidosulphonic acid of the formula (I) where R=OH, —C₆H₄—CH₃(tolyl) andOCH₃ and Z represents hydrogen, sodium and potassium.

In particular, preference is given to the amidosulphonic acid of theformula (I) where R represents OH and Z represents hydrogen.

The stabilizers are used in amounts of 0.02 to 15 mg/l. Preferably, 0.1to 10 mg of stabilizer, in particular 0.2 to 5 mg of stabilizer, per lare used.

It is customary, and to be preferred for the purposes of the invention,that the water phase of the aqueous cooling system additionallycomprises other components which can have an inhibitory action oncorrosion or scale or a dispersive action. Those which may be mentionedby way of example are: 1 to 10 mg/l of zinc ions, 1 to 200 mg/l ofmonomeric or oligomeric molybdate ions, organic phosphates in aconcentration such that the phosphorus content, calculated as phosphate,is in the a range 1 to 20 mg/l of phosphate, monomeric, oligomeric orpolymeric inorganic phosphates at a concentration such that thephosphorus content, calculated as phosphate, is in the range 1 to 20mg/l of phosphate, and nonferrous metal inhibitors, such as triazoles.As further anticorrosion components, the water phase can comprise knownactive compounds, such as alkanolamines, in particular triethanolamine,borates, sorbitol, nitrites, nitrates and silicates. As furtheradditives having corrosion-inhibiting and/or dispersive action, use canbe made of: phosphate esters, polyphosphoric esters, raminophosphates,aminomethylenephosphonic acids, phosphonates, in particularhydroxyalkanediphosphonic acids, hydroxyphosphonoacetic acid,aminoalkylenephosphonic acids, phosphonocarboxylic acids, succinamide,gluconates, polyoxycarboxylic acids and their copolymers, tanninderivatives, lignosuiphates, sulphonated condensation products ofnapthalene with formaldehyde, polyacrylates, polymethacrylates,polyacrylamides, polymaleates, copolymers of acrylic acid or methacrylicacid, maleic acid and acrylamnide, phosphinic-acid-containinghomopolymers and copolymers of acrylic acid and acrylamnide, oligomericphosphinosuccinic acid compounds, sulphomethylated or sulphoethylatedpolyacrylamides and copolymers or terpolymers with acrylic acid, maleicacid, N-butylacrylamide, acrylamidopropionosulphonic acid, maleicanhydride polymers and copolymers, phosphinoalkylated acrylamidepolymers and copolymers with acrylic acid, citric acid,ethercarboxylates or oxidized carbohydrates.

To achieve an optimum corrosion protection, the water phase of theaqueous cooling systems is preferably adjusted to a pH in the range ofabout 7 to about 9. The biocidal oxidizing agents can be metered intothe cooling system continuously or preferably batchwise in the form ofan intermittent treatment.

The aqueous cooling systems can be through flow systems or open orclosed circulation systems. The invention is designed particularly foruse in open circuit systems, since it is especially suitable forcounteracting the problems which occur in such systems of scaleformation, the formation of deposits and/or biological contamination.

The compositions according to the invention can be used in a versatilemanner, for example as scale inhibitors and also corrosion inhibitorsand biocides. Fields of use of such compositions can be, for example:water treatment (e.g. treatment of cooling waters, process waters, gasscrubbing waters, injection waters in secondary oil extraction and watertreatment in mining).

The present invention further relates to a process for water treatmentwhich is characterized in that the composition according to theinvention is introduced into the water to be treated.

The water treatment process is to be illustrated with reference toexamples below:

For example, the compositions according to the invention are added tothe feed water at concentrations between about 0.1 and 10 mg/l of activecompound to prevent depositions and scales when used in cooling systemsusing fresh water cooling.

In cooling circuits, the additives are frequently meteredrate-independently to the make-up water, for scale prevention and/orcorrosion prevention. The concentrations are between about 1 and 100mg/l of active compound in the circulating cooling water.

The invention is further described in the following illustrativeexamples in which all parts and percentages are by weight unlessotherwise indicated.

EXAMPLE 1

In a clear glass flask, 1 l of cooling water having a total hardness of3.0 mmol/l ({circumflex over (=)}17° dGH [German degrees of totalhardness]), of which 80 mol % is carbonate hardness, and K_(S 4,3)=3.2mmol/l ({circumflex over (=)}9° dKH [German degrees of carbonatehardness]) was admixed with 10 mg/l of sodium polyaspartate and 5 ml ofa dilute bleaching liquor solution containing 1000 mg/l as chlorine. ThepH was adjusted to 7.0 using hydrochloric acid, the flask was sealed andstored at room temperature for 24 h.

Similar samples were prepared having the following variants:

pH set to 8.5 by addition of sodium hydroxide solution,

addition of sodium bromide (1 mg/l Br)

addition of 5 mg/l of amidosulphonic acid.

After storage, the chlorine content in the samples was analysed (DPDmethod of Palin)*:

Bromide Amidosulphonic acid Chlorine content No. pH content contentafter 24 h 1 7.0 0 0 0.9 mg/l 2 7.0 0 5 mg/l 2.4 mg/l 3 7.0 1 mg/l 0 0.8mg/l 4 7.0 1 mg/l 5 mg/l 2.4 mg/l 5 8.5 0 0 0.8 mg/l 6 8.5 0 5 mg/l 2.1mg/l 7 8.5 1 mg/l 0 0.3 mg/l 8 8.5 1 mg/l 5 mg/l 2.3 mg/l

*Reference: M. Zimmermann (Editor) Photometrische Metall- undWasseranalyse [Photometric analysis of metals and water], Wissenschaftl.Verlagsgesellschafi, Stuttgart 1974, Method B-C 1/3, variant 2:Determination of “total active chlorine”, including chloramines

Comments on Example 1:

Under pH conditions which are frequently encountered in cooling waters,the reaction of polyaspartic acid (10 mg/l as sodium salt) withbleaching liquor (5 mg/l as chlorine) were studied.

During storage at room temperature, as experiments Nos. 1 and 5 show,the bleaching liquor was >80% reacted, both at pH 7 and at pH 8.5, after24 h; only 0.9 mg/l (pH 7) to 0.8 mg/l (pH 8), in each case measured aschlorine, were recovered.

The addition of bromide additionally intensifies the breakdown,especially at pH 8.5. [Bromide is oxidized under the experimentalconditions present in this application from bleaching liquor tohypobromous acid whose biocidal action, especially at pH 8.5, isconsiderably stronger than that of the bleaching liquor.]

By adding amidosulphonic acid (Experiment Nos. 2, 4, 6, 8), underotherwise identical conditions, the reaction between polyaspartic acidand bleaching liquor (or, with addition of bromide, Experiment Nos. 4and 8, in the additional presence of hypobromous acid) was considerablydecreased: the residual contents of oxidizing agent are higher by afactor of 2.67 (comparison of Experiment Nos. 1 and 2) to 7.67(comparison of Experiments 7 and 8).

Since the chemical reaction of chlorine with PAA, whose progress wasmeasured in this application by the consumption of oxidizing agent, notonly destroys the biocide, but presumably also the polymer, thedegradation reaction is doubly harmful: the biocide added to protect thepolymer from biodegradation is lost and can no longer protect thepolymer and the polymer itself can no longer develop its desiredactivity (corrosion protection and scale protection).

EXAMPLE 2

(See Example 1 for Experimental Procedure)

Variant: Storage of the flasks at 60° C. for 24 h

Results:

Bromide Amidosulphonic No. pH content acid content Chlorine contentafter 24 h 1 7.0 0 0 approximately 0.1 mg/l 2 7.0 0 5 mg/l 1.9 mg/l 37.0 1 mg/l 0 approximately 0.1 mg/l 4 7.0 1 mg/l 5 mg/l 2.5 mg/l 5 8.5 00 approximately 0.1 mg/l 6 8.5 0 5 mg/l 1.2 mg/l 7 8.5 1 mg/l 0approximately 0.1 mg/l 8 8.5 1 mg/l 5 mg/l 1.8 mg/l

Although the present invention has been described in detail withreference to certain preferred versions thereof, other variations arepossible. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the versions contained therein.

What is claimed is:
 1. A composition for water treatment comprising: a)biodegradable organic polymers having repeating succinyl units, b) abiocidal oxidizing agent, and c) an unsubstituted or substitutedamidosulphonic acid, wherein the unsubstituted or substitutedamidosulphonic acid is present in a concentration sufficient to preventor substantially reduce the reaction between a) and b).
 2. Thecomposition of claim 1, wherein the amidosulphonic acid comprisesH₂NSO₃H.
 3. The composition according to claim 1, wherein thebiodegradable organic polymers have repeating succinyl units of thestructures selected from the group consisting of:


4. The composition according to claim 1, wherein the biocidal oxidizingagent is hydrogen peroxide, chlorine, bromine, chlorine dioxide,hypochlorite, hypobromite or ozone; or a reaction product of: (i) acomponent selected from the group consisting of hydrogen peroxide,chlorine, bromine, chlorine dioxide, hypochlorite, hypobromite, andozone; and (ii) water.
 5. A composition for water treatment comprising:a) biodegradable organic polymers having repeating succinyl units b) abiocidal oxidizing agent, and c) an unsubstituted or substitutedamidosulphonic acid, wherein the biodegradable organic polymers containrepeating units selected from the group consisting of the formulae:

wherein the unsubstituted or substituted amidosulphonic acid is presentin a concentration sufficient to prevent substantially reduce thereaction between a) and b).